Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-02-16
2001-07-03
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S202000, C333S219100
Reexamination Certificate
active
06255914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transverse magnetic (TM) mode dielectric resonator and to a TM mode dielectric filter and duplexer using the resonator.
2. Description of the Related Art
A known dielectric filter using a TM mode dielectric resonator is shown in FIG.
13
. Each of the dielectric resonators shown in
FIG. 13
is a dual mode type comprising a plurality of dielectric blocks of short-circuit type TM
110
mode dielectric resonators which are integrally combined in a crisscross fashion. This structure enables each TM mode dielectric resonator to have the function of two TM mode dielectric resonators while being equal in size to one ordinary dielectric resonator of this kind.
Referring to
FIG. 13
, a dielectric filter
101
has four TM dual mode dielectric resonators
102
,
103
,
104
, and
105
, which are arranged in a row in respective cavity casings, with the openings defined by the respective cavity casings facing in the same direction. Metallic panels
106
and
107
are attached to these dielectric resonators so as to cover the openings.
The TM dual mode dielectric resonator
102
has a cavity casing
102
a
having openings on the front and rear sides as viewed in
FIG. 13
, and a dielectric crisscross block
102
XY. The cavity casing
102
a
and the dielectric crisscross block
102
XY are integrally formed of the same dielectric material. A conductor
102
b
is formed on the outer surface of the cavity casing
102
a
except on the front and rear opening edges. The cavity casing l
02
a
with the conductor
102
b
forms a shielded cavity. The dielectric block
102
XY is formed of a horizontal portion
102
X and a vertical portion
102
Y as viewed in FIG.
13
. Thus, the TM dual mode dielectric resonator
102
forms a two-stage resonator. Each of the TM dual mode dielectric resonators
103
,
104
, and
105
has the same structure as the TM dual mode dielectric resonator
102
.
An input loop
108
and an output loop
109
are mounted on the panel
106
. The input loop
108
and the output loop
109
are connected to external circuits via coaxial connectors (not shown).
Coupling loops
107
a
,
107
b
,
107
c
, and
107
d
for coupling each adjacent pair of the TM dual mode dielectric resonators are mounted on the panel
107
.
In dielectric resonators for use in such a dielectric filter, the resonant frequency of each dielectric resonator is determined by the size of the cavity and the size of the dielectric block.
For example, in the case of an ordinary TM
110
mode dielectric resonator having a single vertical dielectric block structure, the resonant frequency becomes lower if the width of the cavity is increased while the width, thickness and height of the dielectric block and the height of the cavity are fixed. The resonant frequency becomes lower if the width or thickness of the dielectric block is increased while the size of the cavity is fixed. Also, when the frequency is fixed, an increase in the unloaded Q of the dielectric resonator is attained by increasing the height of the dielectric block.
In such a case, if the height of the dielectric block is increased, the height of the cavity is necessarily increased. But since a real current flows through the conductor on the cavity casing surface in the TM
110
mode dielectric resonator, the loss in the conductor on the cavity casing surface becomes larger when the size of the cavity casing is increased. However, the increase in unloaded Q achieved by enlarging the cavity is sufficiently large to compensate for the loss in the conductor on the cavity casing surface. Consequently, the unloaded Q becomes higher when the height of the dielectric block is increased.
If the loss in the conductor on the cavity casing surface can be reduced, the unloaded Q can be further increased while limiting the increase in the height of the dielectric block. Therefore, there has been a need for a dielectric resonator designed to have reduced loss in the conductor on the cavity casing surface.
In the TM dual mode dielectric resonator shown in
FIG. 13
, when the sizes of the vertical and horizontal portions of the dielectric block are adjusted to obtain a predetermined frequency, the size of the cavity is also affected. To increase the unloaded Q, therefore, it is necessary to increase both the width and height of the cavity, resulting in an increase in the overall size of the dielectric filter. Also, the resonant frequency becomes lower if the cavity size is increased while the size of the dielectric block is fixed. Therefore, if the size of the cavity is increased, the width or thickness of the dielectric block is necessarily reduced. Thus, in the conventional TM dual mode dielectric resonator, it is difficult to independently change both the unloaded Q and the frequency.
SUMMARY OF THE INVENTION
In view of the above-described problems, the present invention is able to provide a dielectric resonator which has substantially reduced loss in the conductor on the cavity casing surface, and in which the unloaded Q and the resonant frequency can be changed independently of each other.
Another advantage of the present invention is to provide a dielectric filter and a dielectric duplexer having an improved unloaded Q and having a reduced thickness.
To achieve these advantages, according to a first aspect of the present invention, there is provided a TM mode dielectric resonator comprising a shielded-cavity casing having electrical conductivity, and at least one dielectric block disposed in the shielded-cavity casing, wherein electrodes are formed on two surfaces of the dielectric block opposite from each other, and one of the two surfaces on which the electrodes are formed is placed on an inner surface of the shielded-cavity casing.
In this structure, substantially no real current flows in the shielded-cavity casing corresponding to the cavity casing of the conventional TM mode dielectric resonator.
According to a second aspect of the present invention, a plurality of the above-described dielectric blocks are superposed one on another so that at least one of the two surfaces of each dielectric block on which the electrodes are formed is in contact with the adjacent surface of another of the dielectric blocks.
The unloaded Q of the resonator according to the first aspect of the invention can be further improved by using this structure.
According to a third aspect of the present invention, a plurality of the above-described dielectric blocks are superposed one on another so that at least one of the two surfaces of each dielectric block on which the electrodes are formed is opposed to the adjacent surface of another of the dielectric blocks while being spaced apart from the same.
This structure enables use of the dielectric resonator of the present invention as a multi-stage resonator.
According to a fourth aspect of the present invention, a thin-film multilayer electrode formed by alternately superposing thin-film conductors and thin-film dielectrics is used. If the electrodes are formed in this manner, the loss in the electrodes formed on the upper and lower surfaces of the dielectric block in the resonator according to the first aspect of the invention can be reduced, thereby further improving the unloaded Q.
According to a fifth aspect of the present invention, the dielectric block is formed into a cylindrical shape, thereby reducing the loss at the edge of the electrode, as compared to that in the electrode on a dielectric block in the form of a polygonal prism.
According to a sixth aspect of the present invention, the above-described TM mode dielectric resonator is externally coupled to input and output means. A dielectric filter having a high unloaded Q can be obtained by being constructed in this manner.
According to a seventh aspect of the present invention, coupling structures are disposed between the TM mode dielectric resonator and the input and output means.
By changing, adding or removing coupling structures, it is possible to easily control the degree of coupling be
Hidaka Seiji
Ise Tomoyuki
Ishikawa Yohei
Kubota Kazuhiko
Matsui Norifumi
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
Summons Barbara
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